The present disclosure relates to manufacturing processes for washing or coating parts. More particularly, the present disclosure relates to washing or coating parts by immersing the parts in a chemical solution.
In the field of parts finishing, it is typical for parts to go through one or more processes in which chemical solutions are applied to the parts. These processes may include, but are not limited to, the following: cleaning with caustic solution, acid pickling, conversion coating (such as with zinc phosphate or iron phosphate), sealing, rinsing, painting, plating, electrocoating, autophoretic coating, rinsing after painting, etc. It is very common for these processes to including placing parts into contact with chemical solutions. Often these solutions are aqueous liquids.
There are a variety of means of conveying parts through finishing processes. Parts may be hung on racks, and the racks moved through the processes by an overhead monorail conveyor or other similar means. Alternatively, racks may be moved by an indexing conveyor or hoist system. Other systems avoid racks and place parts loosely into containers, and move the containers via monorail or hoist. Another method is to place parts directly onto a belt conveyor.
Racking of parts is labor intensive. Placing parts in containers reduces labor, but still requires efforts to load and unload containers. Also, loading and unloading of containers automatically requires a certain level of sophistication in the equipment. Placing parts on a conveyor belt is often the alternative that requires the least labor, particularly if parts can be loaded automatically with vibratory feed equipment or other similar means.
Parts automatically loaded onto a conveyor belt may be loaded in a manner such that parts are not in contact with each other, or alternately they can be loaded such that parts are piled on the conveyor belt with many parts being in contact with other parts. For a given process length, loading piled parts allows processing of greatly increased quantities while providing parts with the same dwell time in the process. A disadvantage is that parts restrict the ability to deliver chemical solutions to other parts which are located nearer to the middle of the pile. Also, part-to-part contact may result in touch points which are never exposed to solutions, unless the pile is reoriented or adequately agitated to cause the parts to reorient relative to each other.
Parts may be exposed to chemical solutions in a number of ways, including being sprayed or being immersed in chemical solutions or both. The spray may take many different forms, including but not limited to an atomized mist, droplets, a curtain, or a jet. There are distinct advantages and disadvantages to spray application and immersion application. Spraying provides scrubbing action of the solution on the surface of parts. However, recessed areas on parts may receive reduce exposure to the spray. Also, if parts are conveyed in a manner such that some parts block delivery of chemical solutions to other parts, spray methods may not be suitable or at least are less desirable than immersion. Immersion typically gives complete part coverage, even through piled parts. However, immersion may not be as effective as spray at providing liquid movement over the parts. This is particularly true when parts are piled.
It can be seen that, if high volume, low cost finishing is desired, it might be desirable to have a process in which parts are automatically loaded onto a conveyor belt in a piled manner and then moved through an immersion process which produces strong fluid movement through the pile of parts. However, moving loosely piled parts on a conveyor belt through multiple immersions presents several difficulties which are not believed to have been adequately addressed in known immersion systems. A conveyor belt will naturally tend to travel in a straight line between points of support due to the tension in the belt which causes it to move. This path is affected by gravity acting on the conveyor belt, and the manner in which the belt is supported. For a conveyor belt to change direction from a general horizontal direction to a descent into a finishing solution, force would typically need to be applied to the top of the conveyor to overcome the tension in the conveyor belt. Means that apply force to the top of the conveyor belt in the middle of the belt are problematic due to interference with parts being conveyed. Therefore, it has been the normal practice to use conveyor belts which have substantial rigidity in a direction perpendicular to their travel, and to exert downward force on the outer edges of the conveyor belt beyond the portion of the belt that carries parts. Such a conveyor belt is generally more expensive and complex than a belt which does not require lateral rigidity.
Belts which do not possess substantial lateral rigidity may readily be made to change direction as they pass over supports, but any reversal of curvature typically requires applying force to both surfaces of the belt over the width of the belt. Reversed curvature of a belt may be achieved by allowing the belt to sag under the influence of gravity in an unsupported segment of the belt between supports. This is referred to as a catenary, or catenary sag.
Machines that include multiple descents and ascents of the conveyor belt are generally more complex and expensive than machines which move parts in a monotonic path, or a path that does not include reversals of belt curvature. Finally, parts subject to steep ascents or descents may cascade or tumble, which can be detrimental to their uniform conveyance. Flights on the conveyor belt can restrict part movement, but add complexity and interfere with automatic loading.
While disadvantages regarding various prior art systems have been discussed above, there is no intention to exclude or disclaim such systems, or portions or features thereof, from being within the scope of the appended claims. In fact, many features discussed above may be present in a parts immersion apparatus or method as contemplated and as claimed herein.